Short-fibered nonwoven fabrics

ABSTRACT

A fluid dispersion of ultrashort fibers of from 50 to 300 microns in length is applied to a preformed fleece of textilelength fibers, to increase the opacity of the assembly when it is formed into a nonwoven fabric.

United States Patent Inventor Nicholas Newman West Newton, Mass.

Appl. No. 779,318

Filed Nov. 25, 1968 Patented Oct. 26, 1971 Assignee The Kendall Company Boston, Mass.

SHORT-FIBERED NONWOVEN FABRICS 8 Claims,3Drawing Figs.

U.S.Cl 161/170, 19/155, 156/62.2, 161/162 Int. Cl D04h 5/00, B32b 5/16 Field of Search 161/169, 170,15l,153,l52,156,141,162;156/62.2; 19/155 References Cited UNITED STATES PATENTS Sherman Lawrence...

Duvall Graham Pearson et a1. .1

Shaw .1

Primary Examiner-M0rris Sussman Attorney-John F. Ryan ABSTRACT: A fluid dispersion of ultrashort fibers of from 50 to 300 microns in length is applied to a preformed fleece of textile-length fibers, to increase the opacity of the assembly when it is formed into a nonwoven fabric.

SHORT-FIBERED NONWOVEN FABRICS This invention relates to a process for the preparation of bonded nonwoven fabrics, and the products thereof. More particularly, it relates to the preparation of medium or light weight nonwoven fabrics of high capacity, suitable for fashioning into items such as disposable or limited-use garments.

Bonded nonwoven fabrics, comprising dry-assembled, textile-length unspun and unwoven fibrous webs bonded by polymeric binding materials, are produced by a variety of processes and are staple articles of commerce. In addition to numerous industrial applications, they are finding increasing use in the field of disposable items such as garments, sheets, pillowcases, surgical drapes, and the like. Conventional nonwoven fabrics, however, are planar and uniform, not closely resembling the woven fabrics which they are intended to replace. \Additionally, and of paramount importance in disposable clothing, conventional nonwoven fabrics ,of a weight range which may economically be used are undesirably translucent, and lack covering orconcealing power.

Attempts have been made to .remedy this translucency by embossing the surface of the nonwoven fabric, or printing designs thereon, to increase the light-scattering effect. Such attempts are expensive and of limited utility. Recourse has also been had to the use of highly delustered fibers, such as viscose rayon fibers with abnormally high titanium dioxide contents. The opacity and dullness of such .fibers reaches a limit, however, at a rather low level of pigment content, and the increase in opacity of nonwoven fabrics produced therefrom is marginal. The same is true of attempts to opacify nonwoven fabrics by adding clay or other fillers to the binder used to unify the fibrous structure.

It has also been proposed to deposit a layer of paperrnaking fibers, 1,000 microns or more in length, upon a web or fleece of textile-length fibers. Due to the length of papermaking fibers, however, and perhaps also in part to their swollen and hydrated condition, papermaking fibers tend to filter out onto a web of textile length fibers without penetrating into the web sufficiently to form a satisfactory interlocking bond.

It has now been found that ultra short fibers of shorter length than papermaking fibers preferably in substantially unbeaten and unhydrated condition, may be applied to a web of textile-length fibers so as to penetrate into the textile fiber web to an unexpected degree, thus providing a desirable degree of opacification and internal fortification. Such fibers, herein termed ultra short, range in average length from 50 to .3 microns, and are discussed more fully herein below.

The present invention relates to processes for combining ultra short fibers with fibers of textile length to form bonded nonwoven fabrics.

It is therefore an object of the invention to supply an economical and efficient process for fortifying and opacifying nonwoven fabrics of textile length fibers with ultrashort fibers.

It is a more specific object of the invention to provide bonded nonwoven fabrics which are mixtures of textile-length fibers and ultra short fibers wherein the ultrashort fibers are horizontally disposed and are distributed in nonuniform fashionthroughout the textile-length fibers.

It is a further object of the invention to employ in such a process a mixture of ultrashort fibers of different lengths, so that the shorter ultrashort fibers are preferentially deposited in the interior of the nonwoven fabric.

Basically, the steps involved in the process comprise:

l. Assembling textile-length fibersinto a dry, unspun and ,un woven web as by means of cards, garnetts, air-lay 'devices, or the like. i

2. Saturating the fibrous web with an appropriatebinder solution containingultrashort fibers suspended therein in dilute concentration, said ultrashort fibers being substantially unbeaten, unhydrated, and uniformly distributed in a nonagglomerated condition.

3. Mechanically removing a major portion of the binder solution from the web while leaving the ultrashort fibers upon and within the web.

4. Completing the drying ofthe bonded nonwoven fabric.

As an alternative to step 2 above, the ultrashort fibers may be applied to the web of textile-length fibers in simple aqueous suspension, with the binder being applied in a subsequent flooding or spraying application. Or if desired, a part of of the ultrashort fiber charge may be applied to the textile fiber web from aqueous suspension, with the balance of the ultrashort fiber being suspended in the binder solution. Engineering considerations will dictate the method of choice: for example, if the binder solution is to be applied by an atomized spray, it is desirable that the ultrashort fibers be combined with the textile-length fibers in an operation separate from the bonding step.

The invention will be better understood by reference to the drawings, in which:

FIG. 1 is a schematic representationof an apparatus suitable for the practice of the invention,

FIG. 2 is a cross-sectional representation of a preferred product of the invention, and

FIG. 3 is a cross-sectional representation of another embodiment of theinvention.

Referring to FIG. 1, a web of unspun and unwoven textilelength fibers 10 is shown as being delivered from a supply roll 12 to a porous conveyor screen M. Alternatively, the web 10 may be delivered to the screen 14 directly as it is formed on textile cards, garnetts, or air-lay machines.

By textile-length fibers is meant thosefibers which by virtue of their length may be dry-assembled on textile fiber handling equipment into a coherent, self-sustaining web or fleece. Usually textilelength fibers have a minimum average length of at least one-half inch (12,500 microns), incontrast to conventional paper-making fibers which have an average length of not over l,000-3,000 microns.

The fibrous web is advanced by the conveyor screen I4 to pass underneath a flooder box 16, so arranged that a constant fluid sheet of binder solution containing suspended ultrashort fibers is deposited on the web. The flooder box is fed from a supply tank 20, in whichthe ultrashort fibers are .kept in suspension 18 in the binder solution, preferably by means of constant agitation. Therate of feed of the suspension to the flooder box is,controlled by the valve 2.2.

By ultrashort fibers is meant herein fibers which are. below the lengthof papermaking fibers and which for the purposes of this invention are not beaten, hydrated, or fibrillated to any substantial degree. Suitable fibers average from 50 to 300 microns in length, and may be typified by bleached ground wood pulp which has fibers of varying lengths distributed over that range, or by specially processed ultra short cellulosic fibers known as Solka-Floc, a trademarked namefor fibers supplied bythe Brown Company. In the latter case, thelength of the ultrashort fibers is closely grouped around a mean, and mixtures of such fibers may advantageously be used.

From the flooder box the web is advanced to a device which removes excess liquid saturant, leaving substantial amounts if not all of the ultrashort fibers, deposited] partly upon and partly within the fibrous web, as described below. For most purposed, this extraction of excess saturant may be effected by the use of an ordinary suction box 29, the action of which may be supplemented by a set of table rolls '24, as shown. Such rolls, as in the paper industry, revolve against the lower surface of the screen 114 which supports the wet web, and thus exert a wiping action or even a gentle suction which removes a preponderance .of the saturant, thus expediting subsequent drying, without dragging out any significant amount of ultrashort fibers.

The excess binder solution thus removed, together withany spillage from the headbox, is recovered in the pump or drainagepan 25, whence it is pumped for recovery and reuse of binder solution. Such recovery systems are conventional and are not shown.

The screen M, driven by guide rolls 15, may be washed free of residual binder solution, if desired, by means of a water spray27.

Subsequent drying, and the completion of the setting of the binder, may be accomplished by transferring the partially dried web to an auxiliary screen 26, driven by rolls 28 and 30, upon which it passes under infrared heaters 32. Final drying may be accomplished by a steam-heated dry can 34, or a plurality thereof. The drying process is not critical, and various other drying expedients may be employed. In general it may be said that for the preservation of maximum softness and drape in the final product, undue pressures should be avoided in the drying step as well as in the other stages of the process.

As an alternative process for applying the ultrashort fibers to the textile fiber web, an auxiliary flooder box 17 may be used, shown in dotted lines in FIG. I. The supply tank 21 and control valve 23 correspond to their counterparts and 22 which supply the flooder box 16. The suspension 19 in the supply tank 21 may be a suspension of ultrashort fibers in water, or a suspension of ultrashort fibers of for example 50 microns in length suspended in a binder solution in tank 21 may be supplemented by the application of a second binder suspension from tank 20, said second suspension containing fibers which, though ultrashort, are longer then the fibers in the first flooder box. Various other modifications of the process will occur to those skilled in the art.

Conventional water-dispersed binder systems may be em ployed in the process of this invention, including the various commercially available dispersions of polyacrylic binders, polyvinyls, butadiene-styrene polymers, and the like, depending on the particular degree of strength, hand, and elongation which it is desired to realize in the final product. Fire retardants, water repellants, and other finishing auxiliary agents may be compounded with the binder system.

The above process is generally applicable to binder systems which contain my preferred range of between 1 percent and 4 percent of ultrashort fibers. The fibers may be substantially all of the same length, for example 50 microns as in Solka-Floc BW 200, or they may vary in length, as in the case of ground wood pulp. For some purposes, as mentioned above, it is desirable to apply initially a suspension of ultrashort fibers averaging around 50 microns, which penetrate a substantial distance down into the fleece of textile-length fibers, following with an application of ultrashort fibers of greater length, which remain more heavily concentrated on or immediately near the surface of the fleece.

In general, the opacified nonwoven fabrics of this invention may be characterized as stratified, with regard to fiber distribution. This is presumably die to the fact that the fleece of textile-length fibers acts as a filter bed, with the shortest of the ultrashort fibers penetrating a substantial distance into the interior of the fleece. As the descending ultrashort fibers are trapped within the fleece, they impede the descent of other ultrashort fibers, so that there is an enrichment of the upper surface of the fleece, with very flew if any ultrashort fibers becoming trapped in the lower surface of the fleece.

This is shown schematically in FIG. 2, where a nonwoven fabric 40 is shown as composed of a fleece of textile-length fibers 42, with ultrashort 40 micron fibers 44 disposed in generally horizontal alignment with the textile-length fibers, but more heavily concentrated at and near the upper surface of the fleece, where the binder solution ultrashort fiber suspension has been applied. By concentrating a stratum of horizontally disposed ultrashort fibers at or near one surface of a nonwoven fabric, it has been found that a higher opacifying effect, and less stiffening of the fabric, are observed than when ultrashort fibers are mixed with the textile-length fibers in a dry assembling process.

Even more of an opacifying effect is observed when a mixture of ultrashort fibers of varying lengths, or successive deposits of shorter and longer ultrashort fibers, is applied to a fleece of textile-length fibers. Such a product is shown in FIG. 3, where the shortest (50 micron) fibers have penetrated into, but not through, the fleece while the longer ultrashort fibers 46 remain at or very close to the surface of the fabric 41.

FIG. 2 and 3 are schematic and idealized in the sense that any showing of the binder has been omitted, for clarity. Also, the fiber density in an actual product will be greater, and there will be in most cases a greater degree of fiber intermingling. In FIGS. 2 and 3, the shortest (50 micron) fibers are strippled, the longer ultrashort fibers are cross hatched. The invention will be illustrated by the following examples.

EXAMPLE I.

Using apparatus similar to that of FIG. 1 with a single flooder box, a carded fleece of 1.5 denier 1.5 inch rayon weighing 26 grams per square yard was supported on the screen conveyor 14 and was flooded with a suspension of l percent Solka-Floc microns in length in an aqueous dispersion of an 1 L5 percent concentration of acrylic binder. The flooder box supplied 20 gallons of suspension per minute to the 50 inch wide web, and the linear speed was 40 feet per minute. The dried product resembled that of FIG. 2, with the ultrashort fibers concentrated in the upper portion, and particularly near the surface, of the fabric, with the lower surface of the fabric being predominantly composed of textile-length fibers.

The product weighed 53 grams per square yard and consisted of approximately 20 percent binder, 40 percent textilelength rayon, and 3 I percent ultashort fibers.

EXAMPLE II.

Using the same carded fleece as in example I, but with two flooder boxes arranged in tandem above the conveyor screen, there was applied first an 1 L5 percent dispersion of an acrylic binder containing 1 percent of suspended 50 micron Solka-Floc at a rate of 8 gallons per minute, followed by an application of 11.5 percent acrylic binder dispersion containing 1 percent of suspended 80 micron Solka-Floc. The speed again was 40 feet per minute. The dried product resembled that of FIG. 3, with the longer of the ultrashort fibers concentrated at the upper surface of the fabric, the shorter fibers extending down into the fabrics, and the bottom surface of the fabric being composed predominantly of textile-length fibers.

The product weighed 58 grams per square yard and consisted of approximately 20 binder, 45 percent textile-length rayon, and 35 percent ultrashort fibers.

EXAMPLE III.

Again using two flooder boxes, a carded web of viscose rayon fibers, 1.5 denier and L5 inches long, weighing 24 grams per square yard, was first treated with an aqueous suspension of 3 percent Solka-Floc 80 microns in fiber length. This was followed by an application from the second flooder box of a 15 percent aqueous dispersion of an acrylic binder. The dried product weighed 68 grams per square yard, consisting of 24 grams each of 1.5 inch rayon fibers and 80 micron ultrashort fibers, with 20 grams of binder.

The degree of opacity desired will vary with the particular end use to which the product is to be put. Considering fiber content only, and neglecting the binder, it is seen that the fabric of example I contained 61 percent textile-length fibers, 39 percent ultrashort fibers. In example II, the corresponding FIGS. are 56 percent and 44 percent: in example III, 50 percent each. It has been found in general that desirable enhancements in opacity may be observed when the ultrashort fibers in fabrics of this invention constitute between 25 percent and 60 percent of the total fiber content.

As a measure of opacity, it is desirable to use a Bausch and Lomb Opacimeter 33-88-l2, as set forth in Textile Research Journal, Vol. 38, No. 1, Jan., l968, page 8. Therein, a value for 60x64 cotton sheeting is given as 0.63. For a nylon-rayon nonwoven fabric weighing 67 grams per square yard the given.

a value is 0.44. For rayon nonwoven fabrics of 50 to 60 grams per square yard, made from the same fiber and binder as in example I and II but with no ultrashort fiber content, values in the range of 0.40-0.45 may be expected. For the product of example I, the value was 0.69; for examples ll and Ill, 0.71. Using this method of measurement, opacity values of 60 or higher are considered acceptable. Thus a valuable and desirable increase in opacity is realized by a process which is both economical and efficient.

Having thus described my invention, I claim: 1. The process for improving the opacity, softness and flexibility of nonwoven fabrics which comprises assembling a dry-laid fleece of unspun and unwoven textilelength fibers as a fibrous substrate, flooding onto said fleece at least one aqueous dispersion comprising between 99 percent and 96 percent aqueous phase including a polymeric binder and between 1 percent and 4 percent of substantially unhydrated and unbeaten ultrashort cellulosic fibers of between 50 and 300 microns in length, said flooding causing said aqueous solution to pass through the fleece so that the ultrashort fibers are filtered out of said dispersion and at least a portion of the binder dispersion is retained by said fleece and the ultrashort fibers are deposited in generally horizontal orientation upon and within the body of said fleece extending down into said fibrous substrate and intermingling with the fibers thereof, and drying the fabric thus formed. 2. The process according to claim 1 in which multiple applications of aqueous dispersion of bonding agent and ultrashort fiber are made to the fleece of textile-length fibers.

3. The process according to claim 2 in which the ultrashort fibers are of shorter length in the initial application of aqueous dispersion and of greater length in subsequent applications.

4. The process according to claim l in which the-ultrashort fibers are of mixed lengths distributed between 50 and 300 microns.

5. A soft conformable bonded nonwoven fabric comprising a fleece of textile-length fibers averaging not less than one-half inch in length and unbeaten unhydrated ultrashort cellulosic fibers of between 50 and 300 microns in length,

said ultrashort fibers being intermingled with and bonded to said textile-length fibers throughout at least a portion of the depth of said fleece,

and said ultrashort fibers being more hightly concentrated at one surface of said fleece than at the other surface of said fleece.

6. The product according to claim 5 in which the ultrashort fibers are of different lengths, and the longer of the ultrashort fibers are more heavily concentrated at one surface of the fabric than are the shorter fibers.

7. The product according to claim 5 in which between 25 percent and 60 percent of the total fiber content consists of ultrashort fibers.

8. The product according to claim 5 wherein at least some of the ultrashort fibers are bonded to each other.

II! t i t t 

2. The process according to claim 1 in which multiple applications of aqueous dispersion of bonding agent and ultrashort fiber are made to the fleece of textile-length fibers.
 3. The process according to claim 2 in which the ultrashort fibers are of shorter length in the initial application of aqueous dispersion and of greater length in subsequent applications.
 4. The process according to claim 1 in which the ultrashort fibers are of mixed lengths distributed between 50 and 300 microns.
 5. A soft conformable bonded nonwoven fabric comprising a fleece of textile-length fibers averaging not less than one-half inch in length and unbeaten unhydrated ultrashort cellulosic fibers of between 50 and 300 microns in length, said ultrashort fibers being intermingled with and bonded to saId textile-length fibers throughout at least a portion of the depth of said fleece, and said ultrashort fibers being more highly concentrated at one surface of said fleece than at the other surface of said fleece.
 6. The product according to claim 5 in which the ultrashort fibers are of different lengths, and the longer of the ultrashort fibers are more heavily concentrated at one surface of the fabric than are the shorter fibers.
 7. The product according to claim 5 in which between 25 percent and 60 percent of the total fiber content consists of ultrashort fibers.
 8. The product according to claim 5 wherein at least some of the ultrashort fibers are bonded to each other. 